Noise mitigating microphone system and method

ABSTRACT

A microphone system has a base coupled with first and second microphone apparatuses. The first microphone apparatus is capable of producing a first output signal having a noise component, while the second microphone apparatus is capable of producing a second output signal. The first microphone apparatus may have a first back-side cavity and the second microphone may have a second back-side cavity. The first and second back-side cavities may be fluidly unconnected. The system also has combining logic operatively coupled with the first microphone apparatus and the second microphone apparatus. The combining logic uses the second output signal to remove at least a portion of the noise component from the first output signal.

PRIORITY

This patent application is a continuation of utility patent applicationSer. No. 12/546,073, entitled, “Noise Mitigating Microphone System andMethod,” filed on Aug. 24, 2009, and naming Kieran P. Harney, JasonWeigold, and Gary Elko as inventors, the disclosure of which isincorporated herein, in its entirety, by reference, which is acontinuation in part of utility patent application Ser. No. 11/492,314entitled “Noise Mitigating Microphone System and Method” filed Jul. 25,2006, and naming Kieran P. Harney, Jason Weigold, and Gary Elko asinventors, the disclosure of which is incorporated herein, in itsentirety, by reference.

Utility patent application Ser. No. 11/492,314, in turn, claims priorityfrom provisional U.S. patent application No. 60/710,515, filed Aug. 23,2005, entitled, “MICROPHONE SYSTEM,” and naming Kieran Harney as theinventor, the disclosure of which is incorporated herein, in itsentirety, by reference.

FIELD OF THE INVENTION

The invention generally relates to microphones and, more particularly,the invention relates to improving the performance of microphones.

BACKGROUND OF THE INVENTION

Condenser microphones typically have a diaphragm that forms a capacitorwith an underlying backplate. Receipt of an audible signal causes thediaphragm to vibrate to form a variable capacitance signal representingthe audible signal. It is this variable capacitance signal that can beamplified, recorded, or otherwise transmitted to another electronicdevice.

Problems arise, however, when the microphone is subjected to amechanical shock. Specifically, mechanical shocks can cause thediaphragm to vibrate in a manner that degrades the microphone outputsignal.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, a microphone systemhas a base coupled with first and second microphone apparatuses. Thefirst microphone apparatus is capable of producing a first output signalhaving a noise component, while the second microphone apparatus iscapable of producing a second output signal. The first microphoneapparatus may have a first back-side cavity and the second microphonemay have a second back-side cavity. The first and second back-sidecavities may be fluidly unconnected. The system also has combining logicoperatively coupled with the first microphone apparatus and the secondmicrophone apparatus. The combining logic uses the second output signalto remove at least a portion of the noise component from the firstoutput signal.

The second output signal may have, among other things, data relating tothe mechanical response of the first microphone apparatus. Moreover, thesecond microphone apparatus may have a diaphragm and a cap acousticallysealing the diaphragm. Alternatively, the diaphragm may be exposed to aspace to which another diaphragm in the system is exposed. In someembodiments, the second microphone apparatus has a microphone and a lowpass filter.

Various embodiments of the first microphone apparatus have a firstmicrophone, while the second microphone apparatus has a secondmicrophone. The second microphone may be configured to have a lowfrequency cut-off that is greater than the low frequency cut-off of thefirst microphone. In addition, the first microphone may have a firstdiaphragm and a first circumferential gap defined at least in part bythe first diaphragm, while the second microphone may have a seconddiaphragm and a second circumferential gap defined at least in part bythe second diaphragm. The second circumferential gap illustratively isgreater than the first circumferential gap. This second gap effectivelymitigates low frequency audio components while the filter, if used,substantially removes or mitigates remaining audio component.

To remove at least a portion of the noise components produced bymechanical shock, the second microphone apparatus may have a microphoneand a signal transformation module (e.g., an adaptive filter).

In accordance with another embodiment of the invention, a microphonesystem has a base coupled with first and second microphone apparatuses.The first microphone apparatus is capable of producing a first outputsignal and has a first microphone with a first mechanical response. In asimilar manner, the second microphone apparatus is capable of producinga second output signal and has a second microphone with a secondmechanical response. The first microphone apparatus may have a firstback-side cavity and the second microphone may have a s back-sidecavity. The first and second back-side cavities may be fluidlyunconnected. The system also has combining logic operatively coupledwith the first and second microphone apparatuses. The combining logiccombines the first and second output signals to produce an output audiosignal. The first and second mechanical responses illustratively areeffectively the same.

Among other things, the combining logic may include a subtractor thatsubtracts the second output signal from the first output signal. Inother embodiments, the combining logic may have an adder.

In accordance with another embodiment of the invention, a method ofproducing an output audio signal from a microphone system provides abase having a first microphone for generating a first microphone outputsignal (having an audio component and a mechanical component) inresponse to an input audio signal and a mechanical signal. The base alsohas a second microphone for generating a second microphone output signalin response to the mechanical signal. The first and second microphonesmay have back-side cavities that are fluidly unconnected to one another.The method uses information from the second microphone output signal toremove at least a portion of the mechanical component from the firstmicrophone output signal.

The second microphone output signal may have a second audio component.In that case, the method may remove at least a portion of the secondaudio component from the second microphone output signal. In addition,the method may adaptively filter the second microphone output signal.Among other ways, the method may remove at least a portion of the secondaudio component from the second microphone output signal beforeadaptively filtering.

Illustrative embodiments of the invention are implemented as a computerprogram product having a computer usable medium with computer readableprogram code thereon. The computer readable code may be read andutilized by a computer system in accordance with conventional processes.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing advantages of the invention will be appreciated more fullyfrom the following further description thereof with reference to theaccompanying drawings wherein:

FIG. 1 schematically shows a base having a microphone system configuredin accordance with illustrative embodiments of the invention.

FIG. 2 schematically shows a cross-sectional view of a MEMS microphonethat may be used with illustrative embodiments of the invention.

FIG. 3A schematically shows a plan view of the microphone system inaccordance with a first embodiment of the invention.

FIG. 3B schematically shows a plan view of the microphone system inaccordance with a second embodiment of the invention.

FIG. 3C schematically shows a cross-sectional view of the microphonesystem shown in 3A, in accordance with illustrative embodiments of thepresent invention.

FIG. 3D schematically shows a cross-sectional view of an alternativemicrophone system with a lid, in accordance with embodiments of thepresent invention.

FIG. 3E schematically shows a cross-sectional view of an alternativemicrophone system made on a single die, in accordance with furtherembodiments of the present invention.

FIG. 3F schematically shows a cross-sectional view of an additionalalternative microphone system in accordance with further embodiments ofthe present invention.

FIG. 4A schematically shows the frequency response for the primarymicrophone in the microphone system of illustrative embodiments of theinvention.

FIG. 4B schematically shows the frequency response for the correctionmicrophone in the microphone system of illustrative embodiments of theinvention.

FIG. 5 schematically shows additional details of illustrativeembodiments of the microphone system, including filters and combinationlogic.

FIG. 6 shows a process used by the microphone system of FIG. 1 toproduce an audible signal in accordance with illustrative embodiments ofthe invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In illustrative embodiments, a microphone system has a primarymicrophone and a correction microphone coupled to the same base to bothreceive the same noise signals (e.g., mechanical shock signals) andreact in a corresponding manner. To improve the quality of the outputaudio signal it produces, the microphone system uses noise signalsdetected by the correction microphone to remove significant amounts ofnoise from the signal produced by the primary microphone. As a result,the output audio signal should have less noise than if not processed andnoise is present. Details of illustrative embodiments are discussedbelow.

FIG. 1 schematically shows a mobile telephone acting as a base 10 forsupporting a microphone system 12 configured in accordance withillustrative embodiments of the invention. To that end, the mobiletelephone (also identified by reference number 10) has a plastic body 14containing the microphone system 12 for producing an output audiosignal, an earpiece 16, and various other components, such as a keypad,transponder logic and other logic elements (not shown). As discussed ingreater detail below, the microphone system 12 has a primary microphone18A and a correction microphone 18B that are both fixedly secured invery close proximity to each other, and fixedly secured to the telephonebody 14. More generally, both microphones 18A and 18B illustratively aremechanically coupled to each other (e.g., via the base 10 or a directconnection) to ensure that they receive substantially the samemechanical signals. For example, if the telephone 10 is dropped to theground, both microphones 18A and 18B should receive substantiallyidentical mechanical/inertial signals representing the movement andsubsequent shock(s) (e.g., if the telephone 10 bounces several timesafter striking the ground) of the telephone 10.

In alternative embodiments, the microphone system 12 is not fixedlysecured to the telephone body 14—it may be movably secured to thetelephone body 14. Since they are mechanically coupled, both microphones18A and 18B nevertheless still should receive substantially the samemechanical signals as discussed above. For example, the two microphones18A and 18B may be formed on a single die that is movably connected tothe telephone body 14. Alternatively, the microphones 18A and 18B may beformed by separate dies packaged together or separately.

The base 10 may be any structure that can be adapted to use amicrophone. Those skilled in the art thus should understand that otherstructures may be used as a base 10, and that the mobile telephone 10 isdiscussed for illustrative purposes only. For example, among otherthings, the base 10 may be a movable or relatively small device, such asthe dashboard of an automobile, a computer monitor, a video recorder, acamcorder, or a tape recorder. The base 10 also may be a surface, suchas the substrate of a single chip or die, or the die attach pad of apackage. Conversely, the base 10 also may be a large or relativelyunmovable structure, such as a building (e.g., next to the doorbell of ahouse).

FIG. 2 schematically shows a cross-sectional view of a MEMS microphone(identified by reference number 18) generally representing the structureof one embodiment of the primary and correction microphones 18A and 18B.Among other things, the microphone 18 includes a static backplate 22that supports and forms a capacitor with a flexible diaphragm 24. Inillustrative embodiments, the backplate 22 is formed from single crystalsilicon, while the diaphragm 24 is formed from deposited polysilicon. Aplurality of springs 26 (not shown well in FIG. 2, but more explicitlyshown in FIGS. 3A and 3B) movably connect the diaphragm 24 to thebackplate 22 by means of various other layers, such as an oxide layer28. To facilitate operation, the backplate 22 has a plurality ofthroughholes 30 that lead to a back-side cavity 32. Depending on theembodiment and its function, the microphone 18 may have a cap 34.

Audio signals cause the diaphragm 24 to vibrate, thus producing achanging capacitance. On-chip or off-chip circuitry (not shown) convertsthis changing capacitance into electrical signals that can be furtherprocessed. It should be noted that discussion of the microphone of FIG.2 is for illustrative purposes only. Other MEMS or non-MEMS microphonesthus may be used with illustrative embodiments of the invention.

One function of the primary microphone 18A is to produce a primarysignal having an audio component and a (zero or non-zero) noisecomponent. This noise component can include, among other things, 1) amechanical portion and 2) audio responses to the mechanical portion ofthe noise component. For example, the mechanical portion of the noisecomponent could be the response of the microphone when it is dropped tothe ground (i.e., its diaphragm 24 moves as an inertial response). Asanother example, the audio response to the mechanical portion of thenoise signal may be the initial sound and resultant of echoes generatedwhen the microphone/base 10 strikes the ground. Alternatively, themechanical portion of the noise component could be the response of themicrophone to wind (e.g., wind entering the mouthpiece of thetelephone). The primary microphone 18A also may be packaged or capped,as shown, (e.g., a post-processing cap or in-situ cap) with athrough-hole to permit ingress of audio signals.

One function of the correction microphone 18B is to generate acorrection signal that can be used to substantially mitigate much of thenoise component of the primary signal. This mitigation may remove asignificant portion, or a relatively small portion, of the noisecomponent of the primary signal. Various embodiments, however,preferably remove substantially all of the discussed noise components.Removing the noise component should enhance the quality (e.g., thesignal to noise ratio) of the ultimate output signal.

The overall amount and type of mitigation may depend on the application.For example, some embodiments remove the mechanical portion of a noisecomponent only. Other embodiments remove both the mechanical portion andits audio response. Yet other embodiments may remove the audio responseportion of the noise signal only.

The correction microphone 18B may be considered to act as an effectiveaccelerometer within the microphone system 12. Accordingly, in thiscontext, the term “microphone” may be used generally to include otherdevices, such as inertial sensors. Regardless its exact name, thecorrection microphone 18B assists in mitigating inertial based noise(i.e., signals causing undesired diaphragm displacement and relatednoise). In some embodiments, rather than using the discussed correctionmicrophone 18B, the microphone system 12 thus has an accelerometer, suchas one or more one, two, or three axis IMEMS accelerometers produced anddistributed by Analog Devices, Inc. of Norwood, Mass.

The primary microphone 18A and correction microphone 18B preferably areformed to have substantially identical responses to audio and noisesignals discussed herein. To that end, illustrative embodiments producetwo microphones 18A and 18B using substantially identical fabricationprocesses and materials (e.g., silicon-on-insulator technology, orconventional non-SOI surface micromachining processes that depositlayers on a silicon wafer substrate). Accordingly, to the extent theycan as consistent with various discussed embodiments, the microphones18A and 18B should have substantially identical diaphragm masses,backplates, hole sizes, material, etc. . . . Alternative embodiments,however, may use different microphones 18A and 18B that are calibratedto perform the functions discussed herein.

As discussed in greater detail below with regard to FIG. 6, illustrativeembodiments combine the correction signal with the primary signal toremove the noise component from the primary signal. Among other ways,illustrative embodiments may subtract the correction signal from theprimary signal. Accordingly, to avoid subtracting the intended audiosignal from the primary signal, illustrative embodiments of thecorrection signal substantially do not include the noted audio component(e.g., it may include a significantly mitigated version of the audiocomponent). If the correction signal substantially has the audiocomponent, it would undesirably cancel or otherwise substantiallymitigate the audio component from the primary signal, thus substantiallyundercutting one advantage of various embodiments of the system.

Various embodiments therefore physically shield the correctionmicrophone 18B from the input audio signal. In so doing, the correctionmicrophone diaphragm 24 receives mechanical (or related) signals, butdoes not receive the audio signal. To physically shield the diaphragm24, the correction microphone 18B may 1) have a cap 34 that provides anacoustic seal (i.e., shielding the correction microphone diaphragm 24)to the diaphragm 24, 2) be contained within a sealed package, or 3) havesome other physical means for preventing the input audio signal fromcontacting its diaphragm 24.

Other embodiments, however, logically shield the diaphragm 24 of thecorrection microphone 18B from the input audio signal. If that diaphragm24 is logically shielded, then the diaphragms 24 of both of thecorrection microphone 18B and the primary microphone 18A may be exposedto a common space (e.g., the space through which the desired audiosignal traverses). In other words, both diaphragms 24 may receiveessentially the same audio input signal. FIGS. 3A and 3B schematicallyshow two embodiments that provide this functionality.

FIG. 3A schematically shows a plan view of the microphone system 12 inaccordance with a first embodiment that logically shields the correctionmicrophone diaphragm 24. Specifically, the microphone system 12 includesthe primary and correction microphones 18A and 18B fixedly secured to anunderlying printed circuit board 36, and logic 38 (see FIG. 5) forimproving the quality of audio signals received by the primarymicrophone 18A. Because it is a plan view, FIG. 3A shows the respectivediaphragms 24 of the microphones 18 and 18B and their springs 26. Thisconfiguration of having a diaphragm 24 supported by discrete springs 26produces a gap between the outer parameter of the diaphragm 24 and theinner parameter of the structure to which each spring 26 connects. Thisgap is identified in FIG. 3A as “gap 1” for the primary microphone 18A,and “gap 2” for the correction microphone 18B.

As mentioned above, and as shown in FIG. 3C, in some embodiments, theprimary (e.g., 18A) and correction microphones (e.g., 18B) may be formedon or secured to a single substrate or base, for example, the circuitboard 36. To that end, the circuit board 36 may be used to segment orisolate the back-side cavities 32A and 32B of the primary microphone 18Aand the correction microphone 18B from one another. In other words, insome embodiments, the back-side cavities 32A/32B may be fluidlydisconnected from one another (e.g., they do not share a common volume;the back-side cavities are not fluidly connected). In this manner, theprimary microphone 18A and the correction microphone 18B may by exposedto the same audio signal without interference from one another (e.g.,the motion of the diaphragms 24, changes in pressure within theback-side cavities 32A/32B, etc.).

In addition to the segmented back-side cavities 32A/32B mentioned above,one or both of the microphones 18A/18B may also have caps (e.g., caps34A and 34B, respectively). For example, the primary microphone 18A mayhave a cap 34A with an opening to allow the audio signal to reach thediaphragm 24, and the correction microphone 18B may have a closed cap34B (e.g., with no opening) to physically shield the microphone 18Band/or diaphragm 24 from the audio signal. Alternatively, both theprimary microphone 18A and the correction microphone 18B may have caps34A with openings to allow the audio signal to reach the diaphragms 24.In such embodiments, the correction microphone 18B may be logicallyshielded as described above.

As shown in FIG. 3D, some embodiments of the present invention may alsoinclude a lid 320 that spans and covers the microphones 18A and 18B,with segmented back volumes, to seal the microphones 18A/18B as a singlepackage. The lid 320 may have one or more openings 322 that allow theaudio signal to reach the primary microphone 18A. In such embodiments,the microphones 18A and 18B may or may not also have the caps 34A/34Bdescribed above (e.g., the primary microphone may have no cap or an opencap 34A and the correction microphone may have either an open cap 34A, aclosed cap 34B, or no cap).

In some embodiments (e.g., those having no cap or an open cap on thecorrection microphone 18B), the system may have a divider 340 locatedbetween the primary microphone 18A and the correction microphone 18B.This divider 340 physically shields the correction microphone 18B fromthe audio signal entering through the opening 322 in the lid 320.Alternatively, if the correction microphone 18B is not physicallyshielded (e.g., there is no divider 340 and/or the correction microphone18B has no cap or a cap with an opening), the correction microphone 18Bmay be logically shielded as discussed above.

Although the microphones are described above as being separate dies, themicrophones may also be formed on the same die and maintain segmentedvolumes, as shown in FIG. 3E. In such embodiments, the microphones330A/330B may be formed on or otherwise secured to a package base 310,such as an FR-4 base. The package base 310 may then, in turn, be securedto the telephone or the circuit board 36 discussed above. Like theembodiments described above, embodiments formed on the same die may alsoinclude caps 34A/34B. For example, the primary microphone 18A may havean open cap 34A and the secondary microphone may have a closed cap 34B.

FIG. 3F shows a cross-sectional view of an additional embodiment of thepresent invention, in which the audio signal enters the primarymicrophone 18A through the bottom of the microphone 18A. To that end,the substrate 36 may have an opening 360 (a “bottom port”) to theback-side cavity 32A, which effectively becomes a front volume. The areabehind the diaphragm now serves the function of a back volume. Theopening 360 thus allows the audio signal to enter what formerly acted asa back volume, the back-side cavity 32A, and interact with the diaphragm24 (e.g., cause the diaphragm to vibrate), as described above.

Additionally, the substrate 36 may also have a similar opening (notshown) for the correction microphone 18B. If the substrate 36 does nothave an opening for the correction microphone 18B, the correctionmicrophone will be physically shielded from the audio signal (e.g., ifthe lid 350B described below does not have an opening). If the substrate36 does have an opening for the correction microphone 18B, thecorrection microphone may be logically shielded, as discussed above.

The primary and correction microphones 18A/18B of this embodiment mayalso have lids 350A and 350B. In a manner similar to the caps 34A/34Band lid 320 discussed above, the lids 350A/350B may or may not haveopenings to allow the audio signal to reach the microphones 18A/18B fromthe top. For example, the primary microphone lid 350A may have anopening and the correction microphone lid 350B may not. Alternatively,the correction microphone lid 350B may have an opening and the primarymicrophone lid 350A may not, or both may have or not have an opening.

As mentioned in greater detail below and as shown in FIGS. 4A and 4B,some embodiments of the present invention can utilize microphones havingdifferent low frequency cut-offs. It is important to note that segmentedand/or fluidly unconnected back-side cavities aid in creating thedifferent low frequency cut-offs shown in FIGS. 4A and 4B. Inparticular, the segmented and/or fluidly unconnected back-side cavitiesmay allow each of the microphones 18A/18B to have separate andindependent air leakage rates past the diaphragms 24, as described ingreater detail below.

As known by those skilled in the art, it is generally desirable tominimize the size of that gap (e.g., gap 1) to ensure that themicrophone can respond to low-frequency audio signals. In other words,if the gap is too large, the microphone may not be capable of detectingaudio signals having relatively low frequencies. Specifically, withrespect to the frequency response of a microphone, the location of itslow frequency cut-off (e.g., the 3 dB point) is a function of this gap.FIG. 4A schematically shows an illustrative frequency response curve ofthe primary microphone 18A when configured in accordance withillustrative embodiments of the invention. As shown, the low frequencycut-off is F1, which preferably is a relatively low frequency (e.g.,50-100 Hz, produced by an appropriately sized gap, such as a gap ofabout 1 micron).

It should be noted that this gap is anticipated to have no greater thana negligible impact on the inertial response of the microphone to amechanical signal. Accordingly, although the microphone substantiallydoes not detect audio signals having frequencies below the low frequencycut-off, it still can detect low-frequency inertial signals. Forexample, a microphone having a gap sized to produce a low frequencycut-off of approximately 350 Hz still should detect a mechanical signalhaving a frequency of 150 Hz.

In accordance with one embodiment of the invention, gap 2 (of thecorrection microphone 18B) is larger than gap 1 (of the primarymicrophone 18A). Accordingly, as shown in FIG. 4B (showing the frequencyresponse of the correction microphone 18B), the low frequency cut-off F2(e.g., 2-2.5 KHz, produced by an appropriately sized gap, such as about5-10 microns) of the correction microphone 18B is much higher than thelow frequency cut-off F1 of the primary microphone 18A. As a result, thecorrection microphone 18B does not adequately detect a wider range oflow-frequency audio signals. In other words, increasing the size of gap2 effectively acts as an audio high pass filter for the correctionmicrophone 18B. As discussed in greater detail below, illustrativeembodiments use this effective high pass filter in combination with asubsequent low pass filter 46 to significantly mitigate the response ofthe correction microphone 18B to an input audio signal. Accordingly, thecorrection microphone 18B does not require some means to shield it froman input audio signal (e.g., a cap 34).

There are various ways to make gap 2 larger than gap 1 while stillensuring that both microphones 18A and 18B have substantially identicalresponses to noise signals. Among other ways, the diaphragms 24 may beformed to have substantially identical masses. To that end, thediaphragm 24 of the correction microphone 18B may be thicker than thediaphragm 24 of the primary microphone 18A, while the diameter of thediaphragm 24 of the correction microphone 18B is smaller than thediameter of the diaphragm 24 of the primary microphone 18A.

In other embodiments, the diaphragm masses may be different. In thatcase, internal or external logic may be used to compensate for the massdifferences. For example, if the mass of the correction microphonediaphragm 24 is half that of the primary microphone diaphragm 24, thenlogic may multiply the signal from the correction microphone 18B by ascalar value (e.g., a scalar of two). Logic therefore causes theeffective vibration output of the two microphones to be effectively thesame. Stated another way, the mechanical responses of the twomicrophones may be considered to be effectively the same if 1) they do,in fact, have the same diaphragm masses, or 2) if logic compensates fordiaphragm mass differences to effectively cause them to appear the same(e.g., applying a scalar). In yet other embodiments, the two microphonesmay be entirely different and thus, other logic is required to ensureaccurate results consistent with those discussed herein.

FIG. 3B schematically shows another embodiment in which the gapsdiscussed above are substantially identical. Despite having identicalgaps, the correction microphone 18B still is configured to have afrequency response as shown in FIG. 4B (i.e., having a higher lowfrequency cut-off). To that end, the diaphragm 24 of the correctionmicrophone 18B has one or more perforations or through-holes thateffectively increase the low frequency cut-off. Specifically, the lowfrequency cut-off is determined by the amount of area defined by the gapand the hole(s) through the diaphragm 24. This area thus is selected toprovide the desired cutoff frequency.

In general terms, the embodiments shown in FIGS. 3A and 3B are two of awide variety of means for controlling the air leakage past therespective diaphragms 24. In other words, those embodiments control therate at which air flows past the diaphragm, thus controlling therespective low frequency cut-off points. Those skilled in the arttherefore can use other techniques for adjusting the desired lowfrequency cut-off of either microphone 18A and 18B.

As noted above, illustrative embodiments combine the correction signalwith the primary signal to remove the noise component from the primarysignal. To that end, FIG. 5 schematically shows various elements of themicrophone system 12 for accomplishing those ends. In general, themicrophone system 12 has a primary microphone apparatus 40 having theprimary microphone 18A, and a correction microphone apparatus 42 havingthe correction microphone 18B and two subsequent processing stages 46and 48 (i.e., logic 38). Summation logic 44 (also referred to as“combining logic 44”) combines the outputs from the two microphoneapparatuses to generate an output audio signal that preferably has arelatively low noise component.

As noted above, the correction microphone apparatus 42 generates a noisecomponent for mitigating the noise component of the primary signal. Tothat end, the correction microphone apparatus 42 has 1) a low passfilter 46 for substantially mitigating audio components in thecorrection signal received from the correction microphone 18B, and 2) asignal transformation module 48 for normalizing the audio response tothe mechanical portion of the noise component.

More specifically, although they illustratively are very similar, thetwo microphones 18A and 18B still may have some differences. Forexample, due to the tolerances and limits of their fabrication process,the microphones 18A and 18B may have some minor differences, such as thediaphragm thickness. In fact, as noted herein, some embodiments usedifferent types of devices to serve the function of one or both of themicrophones 18A and 18B (e.g., the correction microphone 18B may be aconventional accelerometer). As another example, the microphones 18A and18B are spaced from each other. The correction microphone 18B thereforemay receive a slightly time delayed version of an audio and/or noisesignal.

Unless normalized, these differences can cause the noise components ofthe two microphones 18A and 18B to vary. If they vary too much, theoutput signal may be corrupted or have a less desirable signal to noiseratio. Illustrative embodiments thus compensate for the impact of theseand other differences between the two microphones 18A and 18B to ensurethat the two microphones 18A and 18B have substantially identical noisecomponents. As noted above, this process may be referred to herein as a“normalization” process.

To that end, the signal transformation module 48 compensates fordifferences between the primary microphone 18A and the correctionmicrophone 18B. In illustrative embodiments, the signal transformationmodule 48 is a conventional adaptive filter. In alternative embodiments,the signal transformation module 48 is a fixed filter. Other devices maybe used to achieve the noted results. The respective filters may be anyconventionally known filter used for the noted purposes. For example, ifused, the adaptive filter may be a least mean squared adaptive filter,also referred to in the art as an “LMS” filter.

Accordingly, in illustrative embodiments, the correction microphoneapparatus 42 generates a signal having no greater than a negligibleamount of the audio signal, thus substantially comprising a noisecomponent. It is this noise component that is used to remove thecorresponding noise component generated by the primary microphoneapparatus 40.

The microphone system 12 therefore has combining logic 44 to combine thetwo signals. Among other things, as noted above, the combining logic 44may include conventional subtraction logic that subtracts the signalgenerated by the correction microphone apparatus 42 from the signalgenerated by the primary microphone apparatus 40. In alternativeembodiments, the combining logic 44 may include an adder. For example,in such embodiments, the microphones 18A and 18B may be positionedwithin the base 10 to generate signals that are 180 degrees out ofphase. More specifically, it is contemplated that one microphone couldbe oriented so that the top surface of its diaphragm 24 faces upwardly,while the other microphone could be oriented so that the top surface ofits diaphragm 24 faces downwardly. Of course, those skilled in the artshould understand that other combining logic 44 may be used tofacilitate system implementation.

It should be noted that the signal generated by the correctionmicrophone apparatus 42 may be considered to be the above notedcorrection signal (i.e., as processed by the filters). In a similarmanner, the signal generated by the primary microphone apparatus 40 alsomay be considered to be the above noted primary signal (i.e., asprocessed by any intervening logic elements, not shown). Accordingly,for simplicity, the output signals of the primary microphone apparatus40 and the correction microphone apparatus 42 respectively are referredto as the primary signal and correction signal.

FIG. 6 shows a process of generating an output audio signal inaccordance with illustrative embodiments of the invention. The processbegins at step 600 by substantially mitigating the audio component fromthe signal generated by the correction microphone 18B. To that end, thecorrection output signal is filtered by the low pass filter 46. As notedabove, when using the embodiments of FIGS. 3A, 3B, or other relatedembodiment, the correction microphone 18B naturally filters signalshaving frequencies that are less than the low frequency cut-off of thelow pass filter 46. For example, if the frequency response of thecorrection microphone 18B has a low frequency cut-off of about 200 Hz,then the low pass filter 46 should similarly have a high frequencycut-off of about 190-200 Hz or greater.

Accordingly, after executing step 600, the correction output signalshould have substantially no non-negligible audio componentcorresponding to an input audio signal. This step may be skipped,however, for those embodiments that shield the diaphragm 24 from theinput audio signal.

Before, contemporaneously with, or after executing step 600, the processnormalizes the audio response to the mechanical portion of the noisecomponent (step 602). Embodiments that do not remove this audio responsemay skip this step. In the general case, however, the signaltransformation module 48 may be retained in the system as an all passfilter that is selectively activated. Alternatively, the signaltransformation module 48 may be eliminated.

At this point in the process, the correction microphone apparatus 42should have generated a correction signal having a noise component thatis substantially identical to the noise component in the primary signal.Both signals thus are forwarded to the summation logic 44 toremove/mitigate the noise component from the primary signal (step 604),thus ending the process. In other words, step 604 removes both themechanical portion of the noise signal, as well as its associated audioresponse.

As noted above, depending upon the orientation of the microphones 18Aand 18B, the summation logic 44 may subtract or add the two signals. Ofcourse, other logic may be used in place of, or in addition to, thediscussed subtraction and addition logic. Accordingly, discussion ofspecific subtraction or addition logic is illustrative only and notintended to limit all embodiments of the invention.

Illustrative embodiments therefore should significantly improve signalto noise ratios over conventional single microphone systems known to theinventors. It should be reiterated that various of the components shownin the drawings are illustrative and not intended to limit the scope ofall embodiments. For example, additional components may be used tooptimize operation. As another example, the microphone system 12 mayhave more than two microphones 18A and 18B or microphone apparatuses.Instead, among other things, the microphone system 12 may have three ormore microphones, or three or more microphone apparatuses. Moreover, oneor more of the microphone apparatuses may include just microphones(e.g., the correction microphone 18B may have just a cap 34 with noaudio input port).

Various embodiments of the invention may at least have portionsimplemented at least in part in any conventional computer programminglanguage. For example, some embodiments may be implemented in aprocedural programming language (e.g., “C”), or in an object orientedprogramming language (e.g., “C++”). Other embodiments of the inventionmay be implemented as preprogrammed hardware elements (e.g., applicationspecific integrated circuits, FPGAs, and digital signal processors), orother related components.

In an alternative embodiment, some portions of the disclosed apparatusand methods (e.g., see the flow chart described above) may beimplemented as a computer program product for use with a computersystem. Such implementation may include a series of computerinstructions fixed either on a tangible medium, such as a computerreadable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk) ortransmittable to a computer system, via a modem or other interfacedevice, such as a communications adapter connected to a network over amedium. The medium may be either a tangible medium (e.g., optical oranalog communications lines) or a medium implemented with wirelesstechniques (e.g., WIFI, microwave, infrared or other transmissiontechniques). The series of computer instructions can embody all or partof the functionality previously described herein with respect to thesystem.

Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Furthermore, suchinstructions may be stored in any memory device, such as semiconductor,magnetic, optical or other memory devices, and may be transmitted usingany communications technology, such as optical, infrared, microwave, orother transmission technologies.

Among other ways, such a computer program product may be distributed asa removable medium with accompanying printed or electronic documentation(e.g., shrink wrapped software), preloaded with a computer system (e.g.,on system ROM or fixed disk), or distributed from a server or electronicbulletin board over the network (e.g., the Internet or World Wide Web).Of course, some embodiments of the invention may be implemented as acombination of both software (e.g., a computer program product) andhardware. Still other embodiments of the invention are implemented asentirely hardware, or entirely software.

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.

What is claimed is:
 1. A microphone system comprising: a base; a firstmicrophone apparatus having a first mechanical response and coupled tothe base, the first microphone apparatus capable of producing a firstoutput signal having a noise component, the first microphone apparatushaving a first back-side cavity and a first diaphragm formed with afirst diaphragm mass; a second microphone apparatus having a secondmechanical response and coupled to the base, the second microphoneapparatus capable of producing a second output signal, the secondmicrophone apparatus having a second back-side cavity and a seconddiaphragm formed with a second diaphragm mass, the first and secondback-side cavities being fluidly unconnected, the first diaphragm massand the second diaphragm being substantially identical such that thefirst and second mechanical responses are effectively the same, thesecond microphone apparatus having a cap acoustically sealing the seconddiaphragm; and combining logic operatively coupled with the firstmicrophone apparatus and the second microphone apparatus, the combininglogic using the second output signal to remove at least a portion of thenoise component from the first output signal.
 2. The microphone systemas defined by claim 1 wherein the second output signal comprises datarelating to the mechanical response of the first microphone apparatus.3. The microphone system as defined by claim 1 wherein the secondmicrophone apparatus comprises a microphone and a low pass filter.
 4. Amicrophone system comprising: a base; a first microphone apparatushaving a first mechanical response and coupled to the base, the firstmicrophone apparatus capable of producing a first output signal having anoise component, the first microphone apparatus having a first back-sidecavity and a first diaphragm formed with a first diaphragm mass; asecond microphone apparatus having a second mechanical response andcoupled to the base, the second microphone apparatus capable ofproducing a second output signal, the second microphone apparatus havinga second back-side cavity and a second diaphragm formed with a seconddiaphragm mass, the first and second back-side cavities being fluidlyunconnected, the first diaphragm mass and the second diaphragm massbeing substantially identical such that the first and second mechanicalresponses are effectively the same; and combining logic operativelycoupled with the first microphone apparatus and the second microphoneapparatus, the combining logic using the second output signal to removeat least a portion of the noise component from the first output signal,wherein the first microphone apparatus comprises a first microphone, thesecond microphone apparatus comprising a second microphone, the secondmicrophone being configured to have a low frequency cut-off that isgreater than the low frequency cut-off of the first microphone.
 5. Themicrophone system as defined by claim 4 wherein the first microphone hasa first diaphragm and a first circumferential gap defined at least inpart by the first diaphragm, the second microphone having a seconddiaphragm and a second circumferential gap defined at least in part bythe second diaphragm, the second circumferential gap being greater thanthe first circumferential gap.
 6. The microphone system as defined byclaim 1 wherein the first microphone apparatus has a first microphonehaving first diaphragm and the second microphone apparatus having asecond microphone with a second diaphragm.
 7. The microphone system asdefined by claim 1 wherein the second microphone apparatus includes amicrophone and a signal transformation module.
 8. A microphone systemcomprising: a base; a first microphone apparatus having a firstmechanical response and coupled to the base, the first microphoneapparatus capable of producing a first output signal having a noisecomponent, the first microphone apparatus having a first back-sidecavity and a first diaphragm formed with a first diaphragm mass; asecond microphone apparatus having a second mechanical response andcoupled to the base, the second microphone apparatus capable ofproducing a second output signal, the second microphone apparatus havinga second back-side cavity and a second diaphragm formed with a seconddiaphragm mass, the first and second back-side cavities being fluidlyunconnected, the first diaphragm mass and the second diaphragm beingsubstantially identical such that the first and second mechanicalresponses are effectively the same; and combining logic operativelycoupled with the first microphone apparatus and the second microphoneapparatus, the combining logic using the second output signal to removeat least a portion of the noise component from the first output signal,wherein the first microphone apparatus comprises a first microphone, thesecond microphone apparatus comprises a second microphone, the firstmicrophone and second microphones having different air leakage rates forproviding the first and second microphones with different low frequencycut-off points.
 9. A microphone system comprising: a base; a firstmicrophone apparatus having a first mechanical response and coupled withthe base and capable of producing a first output signal, the firstmicrophone apparatus including a first microphone having a firstmechanical response and a first back-side cavity and a first diaphragmformed with a first diaphragm mass; a second microphone apparatus havinga second mechanical response and coupled with the base and capable ofproducing a second output signal, the second microphone apparatusincluding a second microphone having a second mechanical response and asecond back-side cavity and a first diaphragm formed with a seconddiaphragm mass, and the first and second back-side cavities beingfluidly unconnected, the first diaphragm mass and the second diaphragmmass being substantially identical, the first and second diaphragmsbeing exposed to a common space, the space through which a desired audiosignal traverses; combining logic operatively coupled with the firstmicrophone apparatus and the second microphone apparatus, the combininglogic combining the first and second output signals to produce an outputaudio signal; and means for removing audible response of mechanicalshock from the first output signal; and the first and second mechanicalresponses being effectively the same.
 10. The microphone system asdefined by claim 9 wherein the combining logic includes a subtractorthat subtracts the second output signal from the first output signal.11. The microphone system as defined by claim 9 wherein the secondmicrophone apparatus comprises an adaptive filter.
 12. The microphonesystem as defined by claim 9 wherein the first output signal comprisesan audio component and a first noise component, the second output signalcomprising a second noise component, the combining logic using thesecond noise component to mitigate the first noise component from thefirst output signal to produce the output audio signal.
 13. A method ofproducing an output audio signal from a microphone system, the methodcomprising: providing a base having a first microphone for generating afirst microphone output signal in response to an input audio signal anda mechanical signal, the first microphone output signal having an audiocomponent and a mechanical component, the first microphone a firstdiaphragm, the first diaphragm having a diaphragm mass, the base alsohaving a second microphone for generating a second microphone outputsignal in response to the mechanical signal, the second microphonehaving a second diaphragm, the first diaphragm having a diaphragm mass,the first and second diaphragm masses being different, the first andsecond microphones having back-side cavities that are fluidlyunconnected to one another; and using information from the secondmicrophone output signal to remove at least a portion of the mechanicalcomponent from the first microphone output signal; compensating for thedifference in diaphragm masses to effectively cause them to appear thesame.
 14. The method as defined by claim 13 wherein the secondmicrophone output signal has a second audio component, using comprisingremoving at least a portion of the second audio component from thesecond microphone output signal.
 15. The method as defined by claim 13further comprising fixed or adaptively filtering the second microphoneoutput signal.
 16. The method as defined by claim 15 wherein the secondmicrophone output signal has a second audio component, using comprisingremoving at least a portion of the second audio component from thesecond microphone output signal before filtering.
 17. The method asdefined by claim 13 wherein the first microphone has a first diaphragmthat defines a first circumferential gap, the second microphone having asecond diaphragm that defines a second circumferential gap, the secondcircumferential gap being greater than the first circumferential gap.18. The method as defined by claim 13 wherein the first microphone has afirst diaphragm, the second microphone having a second diaphragm, themethod exposing the first and second diaphragms to the input audiosignal.
 19. A microphone system comprising: a base; a first microphoneapparatus having a first mechanical response and coupled to the base,the first microphone apparatus capable of producing a first outputsignal having a noise component, the first microphone apparatus having afirst back-side cavity and a first diaphragm formed with a firstdiaphragm mass; a second microphone apparatus having a second mechanicalresponse and coupled to the base, the second microphone apparatuscapable of producing a second output signal, the second microphoneapparatus having a second back-side cavity and a second diaphragm formedwith a second diaphragm mass, the first and second back-side cavitiesbeing fluidly unconnected, the first diaphragm mass and the seconddiaphragm mass being different; and combining logic operatively coupledwith the first microphone apparatus and the second microphone apparatus,the combining logic using the second output signal to remove at least aportion of the noise component from the first output signal.
 20. Themicrophone system as defined by claim 19, further including logicoperable to compensate for the difference in the first and seconddiaphragm masses so as to effectively cause them to appear the same. 21.The microphone system as defined by claim 20, wherein the logic residesin the microphone system.
 22. The microphone system as defined by claim20, wherein the logic resides externally to the microphone system.
 23. Amicrophone system comprising: a base; a first microphone apparatushaving a first mechanical response and coupled with the base and capableof producing a first output signal, the first microphone apparatusincluding a first microphone having a first mechanical response and afirst back-side cavity and a first diaphragm formed with a firstdiaphragm mass; a second microphone apparatus having a second mechanicalresponse and coupled with the base and capable of producing a secondoutput signal, the second microphone apparatus including a secondmicrophone having a second mechanical response and a second back-sidecavity and a first diaphragm formed with a second diaphragm mass, andthe first and second back-side cavities being fluidly unconnected, thefirst diaphragm mass and the second diaphragm mass being different; andcombining logic operatively coupled with the first microphone apparatusand the second microphone apparatus, the combining logic combining thefirst and second output signals to produce an output audio signal. 24.The microphone system as defined by claim 23, further including logicoperable to compensate for the difference in the first and seconddiaphragm masses so as to effectively cause them to appear the same. 25.The microphone system as defined by claim 24, wherein the logic residesin the microphone system.
 26. The microphone system as defined by claim24, wherein the logic resides externally to the microphone system. 27.The microphone system as defined by claim 4, wherein the firstmicrophone apparatus comprises a first microphone, the second microphoneapparatus comprises a second microphone, the first microphone and secondmicrophones having different air leakage rates for providing the firstand second microphones with different low frequency cut-off points. 28.The microphone system as defined by claim 1, wherein the firstmicrophone apparatus comprises a first microphone, the second microphoneapparatus comprises a second microphone, the first microphone and secondmicrophones having different air leakage rates for providing the firstand second microphones with different low frequency cut-off points. 29.The microphone system as defined by claim 8, wherein the firstmicrophone has a first diaphragm and a first circumferential gap definedat least in part by the first diaphragm, the second microphone having asecond diaphragm and a second circumferential gap defined at least inpart by the second diaphragm, the second circumferential gap beinggreater than the first circumferential gap.
 30. The microphone system asdefined by claim 1, wherein the first microphone apparatus has a firstdiaphragm and a first circumferential gap defined at least in part bythe first diaphragm, the second microphone apparatus having a seconddiaphragm and a second circumferential gap defined at least in part bythe second diaphragm, the second circumferential gap being greater thanthe first circumferential gap.